What is wrong then the car jumps or feels as though it is skipping gears? on 2005 Pontiac Grand Prix

There are not any codes.

Asked by for the 2005 Pontiac Grand Prix
Engine misfire, need a tune up!
2 more answers
Engine misfire, need a tune up!
From the frequently reports problems page:

20 reports of Erratic Shifting of the Automatic Transmission

The transmission pressure control solenoid may fail causing erratic shifting. Our technicians tell us that partial dis-assembly of the transmission is necessary to replace a failed pressure control solenoid.